There are known electric alarm clocks, with analog or digital time display, having a tripping device with a setting range of 24 hours. The time-display range extends therein over two times 0 . . . 12 hours, i.e., the display range is traversed twice during the 24-hour setting range of the wakening-signal tripping device. This means that by setting the time for the alarm signal, special attention has to be given to establishing the correct 12-hour interval in which the tripping device is to be actuated. This is usually done by rotating the mechanism of the hands to check in which 12-hour cycle the wakening-signal actuation will occur. Since at least in the case of battery-energized clocks, this setting procedure has to be performed only once during the lifetime of the battery, it is considered acceptable. Nevertheless, it can lead to erroneous settings or at least to a confusion of the user.
It also is significant that a tripping device with an overall setting range of 24 hours usually has a very low actuation speed, which results in a relatively imprecise repetition of the alarm signal and also provides a temporally unreliable contact.
There are also known alarm clocks with a time-display range of 12 hours and a 12-hour setting range of the wakening-signal tripping device. Here a stop switch for the alarm signal is provided, which remanently stops or interrupts the signal. In this way the actuation of the tripping device in one of the 12-hour cycles namely in the undesired cycle is precluded. An automatic reactivation of the wakening-signal tripping device is not possible; before each signal emission the alarm signal circuit has to be prepared by resetting the stop switch.
There are also known electric alarm clocks in which at least one contact is actuatable through the wakening-signal tripping device, the contact resetting a Flip Flop multivibrator circuit, thereby resetting the alarm signal generator. Through a manually actuated button, or through a switch, or through a contact actuatable by the tripping device, the flip-flop circuit is again reset and the signal emission interrupted. Simultaneously the signal readiness for the next signal emission is reestablished. In this case it is necessary, however, to provide a tripping device with a setting range of 24 hours, in ordr to benefit from the advantages of an automatic stand-by circuit.